Porosity in a weld occur when tiny hole appear within the weld bead itself. Porosity occurs due to the presence of oxygen from the atmospheres that enters the weld pool. Shielding gas are a substance that prevents oxygen from entering the weld pool.
In order to prevent the welding metal from contacting with an atmosphere’s oxygen, the shielding gas must form a continuous blanket over the weld. If the shielding gas dont form a continuous blanket over the weld, the oxygen from the atmosphere will enter the metal and cause porosity within the weld. The welder can prevent porosity by controlling the flow rate of the shielding gas that exit the welding nozzle, and by ensuring that the welder utilizes the correct types of shielding gas for the metal that is being welded.
How to Prevent Holes in Welds with Shielding Gas
The flow rate of the shielding gas must be controlled in order to prevent porosity. Shielding gas with an incorrect flow rate can lead to porosity within the weld. Many welding technician believe that a high flow rate of shielding gas will prevent porosity within the weld.
However, if the flow rate of the shielding gas is too high, the shielding gas can create turbulence within the weld pool. Turbulence within the shielding gas can actualy lead to the introduction of air into the weld pool. The welder should avoid turbulence within the shielding gas to ensure that porosity isnt introduced into the weld.
The amount of shielding gas that are required to perform welding tasks depends upon the welding hardware that is to be utilized. For example, welding with thicker wire requires more shielding gas than welding with thinner wire. The thicker wires is used to weld thicker metal materials that require higher amount of heat to complete the welding operation.
As a result, the heat radiating from the metal will push the shielding gas away from the weld. Thus, the welder must introduce more shielding gas at a higher flow rate to compensate for the shielding gas that is forced away from the weld. Additionally, the size of the nozzle from which the shielding gas exit the welding wire will also impact the flow rate of the shielding gas.
Using a large nozzle will require more shielding gas to exit the nozzle than using a smaller nozzle in the welding wire. Using a large nozzle with a low flow rate of shielding gas may not allow for the shielding gas to cover the weld, and the weld may have porosity within it edges. The type of shielding gas that is used in the welding process must be selected such that the requirements of the metal being welded are met.
Different metal have different requirements for shielding gas. For instance, if the metal being welded is mild steel, shielding gas that can be utilized includes both pure carbon dioxide gas, or a blend of argon and carbon dioxide gases. Pure carbon dioxide is a cost-effective shielding gas to utilize.
However, pure carbon dioxide gas creates more spatter during the welding process than a blend of argon and carbon dioxide gas. Argon and carbon dioxide gas blend lead to reduced spatter during the welding process. Additionally, if the metal being welded is aluminum, the welder must utilize shielding gas of pure argon.
If carbon dioxide shielding gas is used, the aluminum will oxidize almost immediate upon contact with the carbon dioxide gas. Thus, the welder must use pure argon when welding aluminum to ensure that the metal is not oxidized. The environment where welding occurs may have an impact upon the shielding gas protection of the weld pool.
For instance, indoor environment typically have still air. Thus, lower flow rates of shielding gases may be used within these environments. However, outdoor environments may expose the shielding gas to the wind.
The wind may blow the shielding gas away from the weld pool. When this occur, the atmosphere’s oxygen will enter the weld pool and create porosity within the weld. Attempts to increase the flow rate of the shielding gas may not be effective in battling the wind.
A portable wind screen can be used to keep the wind from entering the weld pool. Additionally, shortening the distance from the welding wire to the metal can help to ensure that the shielding gas is not blown away from the weld. If the wind is too strong for shielding gas to be effective, the welder can utilize self-shielded flux-core welding wire.
Self-shielded flux-core welding wire contains flux that reacts to form a gas blanket around the weld that shields the weld pool from atmosphere gases. Shielding gas must be regulated appropriately to the welding process. For instance, the gas cylinder that contains the shielding gas should be opened slow.
Additionally, flow meters have a float ball that indicate the flow rate of the shielding gas. The welder must read the center of the float ball to ensure that the flow rate of the shielding gas is accurate. Any hole that are present in the weld beads or discoloration of the metal indicates a problem with the welding equipment.
For instance, a leak in a fitting will reduce the shielding gas pressure. The reduced shielding gas pressure will prevent the shielding gas from protecting the weld. Thus, welding equipment should of been inspected for leak.
The shielding gas and the welding environment must be managed to ensure that the shielding gas prevents the molten metal from contacting the atmosphere’s gas.
